The present invention concerns an apparatus for use in determining the position of and forming of assembling holes in spectacle lenses for rimless spectacles, the assembling holes intended for mounting a bridge and a side bar hinge, and of the type including a holder for the lens and machining means that are movable, preferably in two dimensions, relative to the holder.
The invention furthermore concerns a fixture for spectacle lenses for rimless spectacles and for use in determining the position of and formation of assembling holes in the lens, the assembling holes intended for mounting a bridge and a side bar hinge.
The invention furthermore concerns a packing for use in fixture for spectacle lenses for rimless spectacles and for use in determining position of and formation of assembling holes in the lens, the assembling holes being intended for mounting a bridge and a side bar hinge, the fixture including an opening for fixing the lens at its circumferential edge with the packing disposed between the lens and the fixation opening.
Finally, the invention also concerns a method for fixing spectacle lenses for rimless spectacles by determining position of and formation of assembling holes in the lens, and including:                fixing the lens in a fixture for correct hole centre line orientation;        forming the assembling holes;        mounting a bridge and a side bar hinge in the assembling holes; and        moving machining means, preferably in two dimensions, relative to the holder.        
In the industry of spectacle manufacturing, rimless spectacles have hitherto been problematic for the optician to produce. This is due to that tools and methods up till now put great demands on skill and precision on the part of the optician making assembling holes for mounting bridge and hinge fittings/side bars in the lenses. Among these, a difficulty has particularly appeared at correct positioning of the spectacle lenses in relation to the machining means used for forming the assembling holes. Just a very little turning of axis when positioning a lens in relation to the frame of the machining tool has thus caused a very visible skewness when placing assembling holes and thereby also risk of a distinct skewness in the formed spectacle.
With the known systems, one also desires to use as thin glasses as possible due to weight and appearance of the spectacles. When mounting bridge and hinges occurs in such lenses, the thinner the lenses the greater demands are put on precision.
Furthermore, from the user there are demands to placing the assembling holes/slits as close to the edge of the lens as possible with regard to the general appearance and so that fastening members become less visible in the field of vision. This is particularly the case when the models are relatively small.
Usually, when making lenses it is important to be able to place the spectacle lenses with optical centre correctly in relation to the user. Correct positioning is particularly important on small models where progressive lenses are used. In such lenses, a slight displacement and very small axis deflections of 2-3° may produce big sight problems for the user. By known embodiments, assembling holes in the shape of slits or round holes positioning systems are placed by manual marking of the lens. In some cases, this also occurs under use of simple drill jigs or measuring jigs with basis in manual markings on the lens. This puts great demands on skilled measurement, where the precision depends on the care and the ability residing with the individual optician.
When the optician grinds a lens, there will be tolerances on the so-called box dimensions. Box dimensions are the rectangle where the circumference of the lens can be ground in. A datum line will appear at the same time as the centre line of the height of the box dimension.
The optician will typically measure the width in the box. With the tolerances existing for machines used for grinding today, there is risk of tolerance deviation on the height/width of the box dimension. Therefore, there will be a risk of variations in the box dimensions of the lens. This often entails that the optician grinds lenses with undersize, meaning in turn that the lens becomes too small in relation to a template. When the optician is subsequently to place assembling holes in the lens, this occurs by pressing the lens against a sidewall where the hole is to be made. However, this gives rise to uncertainty at the formation of the assembling holes.